US8514367B2 - Apparatus and method for maintaining immersion fluid in the gap under the projection lens during wafer exchange in an immersion lithography machine - Google Patents

Abstract

An apparatus and method maintain immersion fluid in the gap adjacent to the projection lens during the exchange of a work piece in a lithography machine. The apparatus and method include an optical assembly that projects an image onto a work piece and a stage assembly including a work piece table that supports the work piece adjacent to the optical assembly. An environmental system is provided to supply and remove an immersion fluid from the gap between the optical assembly and the work piece on the stage assembly. After exposure of the work piece is complete, an exchange system removes the work piece and replaces it with a second work piece. An immersion fluid containment system maintains the immersion liquid in the gap during removal of the first work piece and replacement with the second work piece.

Description

RELATED APPLICATIONS

This is a Divisional of U.S. patent application Ser. No. 11/237,721 filed Sep. 29, 2005, which in turn is a Continuation of International Application No. PCT/IB2004/001259 filed Mar. 17, 2004, which claims the benefit of U.S. Provisional Application No. 60/462,499 filed on Apr. 11, 2003. The entire disclosures of the prior applications are incorporated herein by reference in their entireties.

BACKGROUND

Lithography systems are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical lithography system includes an optical assembly, a reticle stage for holding a reticle defining a pattern, a wafer stage assembly that positions a semiconductor wafer, and a measurement system that precisely monitors the position of the reticle and the wafer. During operation, an image defined by the reticle is projected by the optical assembly onto the wafer. The projected image is typically the size of one or more die on the wafer. After an exposure, the wafer stage assembly moves the wafer and then another exposure takes place. This process is repeated until all the die on the wafer are exposed. The wafer is then removed and a new wafer is exchanged in its place.

Immersion lithography systems utilize a layer of immersion fluid that completely fills a gap between the optical assembly and the wafer during the exposure of the wafer. The optic properties of the immersion fluid, along with the optical assembly, allow the projection of smaller feature sizes than is currently possible using standard optical lithography. For example, immersion lithography is currently being considered for next generation semiconductor technologies including 65 nanometers, 45 nanometers, and beyond. Immersion lithography therefore represents a significant technological breakthrough that will likely enable the continued use of optical lithography for the foreseeable future.

After a wafer is exposed, it is removed and exchanged with a new wafer. As currently contemplated in immersion systems, the immersion fluid would be removed from the gap and then replenished after the wafer is exchanged. More specifically, when a wafer is to be exchanged, the fluid supply to the gap is turned off, the fluid is removed from the gap (i.e., by vacuum), the old wafer is removed, a new wafer is aligned and placed under the optical assembly, and then the gap is re-filled with fresh immersion fluid. Once all of the above steps are complete, exposure of the new wafer can begin.

Wafer exchange with immersion lithography as described above is problematic for a number of reasons. The repeated filling and draining of the gap may cause variations in the immersion fluid and may cause bubbles to form within the immersion fluid. Bubbles and the unsteady fluid may interfere with the projection of the image on the reticle onto the wafer, thereby reducing yields. The overall process also involves many steps and is time consuming, which reduces the overall throughput of the machine.

An apparatus and method for maintaining immersion fluid in the gap adjacent to the projection lens when the wafer stage moves away from the projection lens, for example during wafer exchange, is therefore needed.

SUMMARY

An apparatus and method maintain immersion fluid in the gap adjacent to the projection lens in a lithography machine. The apparatus and method include an optical assembly that projects an image onto a work piece and a stage assembly including a work piece table that supports the work piece adjacent to the optical assembly. An environmental system is provided to supply and remove an immersion fluid from the gap. After exposure of the work piece is complete, an exchange system removes the work piece and replaces it with a second work piece. An immersion fluid containment system is provided to maintain the immersion fluid in the gap when the work piece table moves away from the projection lens. The gap therefore does not have to be refilled with immersion fluid when the first work piece is replaced with a second work piece.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in conjunction with the following drawings of exemplary embodiments in which like reference numerals designate like elements, and in which:

FIG. 1 is an illustration of an immersion lithography machine having features of the invention;

FIG. 2 is a cross section of an immersion lithography machine according to one embodiment of the invention;

FIGS. 3A and 3B are a cross section and a top down view of an immersion lithography machine according to another embodiment of the invention;

FIGS. 4A and 4B are cross section views of an immersion lithography machine according to another embodiment of the invention;

FIGS. 5A and 5B are top down views of two different twin wafer stages according to other embodiments of the invention;

FIG. 6A is a top down view of a twin stage lithography machine according to another embodiment of the invention;

FIGS. 6B-6E are a series of diagrams illustrating a wafer exchange according to the invention;

FIG. 7A is a flow chart that outlines a process for manufacturing a work piece in accordance with the invention; and

FIG. 7B is a flow chart that outlines work piece processing in more detail.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic illustration of alithography machine10 having features of the invention. Thelithography machine10 includes aframe12, an illumination system14 (irradiation apparatus), anoptical assembly16, areticle stage assembly18, a workpiece stage assembly20, ameasurement system22, acontrol system24, and a fluidenvironmental system26. The design of the components of thelithography machine10 can be varied to suit the design requirements of thelithography machine10.

In one embodiment, thelithography machine10 is used to transfer a pattern (not shown) of an integrated circuit from areticle28 onto a semiconductor wafer30 (illustrated in phantom). Thelithography machine10 mounts to amounting base32, e.g., the ground, a base, or floor or some other supporting structure.

In various embodiments of the invention, thelithography machine10 can be used as a scanning type photolithography system that exposes the pattern from thereticle28 onto thewafer30 with thereticle28 and thewafer30 moving synchronously. In a scanning type lithographic machine, thereticle28 is moved perpendicularly to an optical axis of theoptical assembly16 by thereticle stage assembly18, and thewafer30 is moved perpendicularly to the optical axis of theoptical assembly16 by thewafer stage assembly20. Scanning of thereticle28 and thewafer30 occurs while thereticle28 and thewafer30 are moving synchronously.

Alternatively, thelithography machine10 can be a step-and-repeat type photolithography system that exposes thereticle28 while thereticle28 and thewafer30 are stationary. In the step and repeat process, thewafer30 is in a constant position relative to thereticle28 and theoptical assembly16 during the exposure of an individual field. Subsequently, between consecutive exposure steps, thewafer30 is consecutively moved with thewafer stage assembly20 perpendicularly to the optical axis of theoptical assembly16 so that the next field of thewafer30 is brought into position relative to theoptical assembly16 and thereticle28 for exposure. Following this process, the images on thereticle28 are sequentially exposed onto the fields of thewafer30, and then the next field of thewafer30 is brought into position relative to theoptical assembly16 and thereticle28.

However, the use of thelithography machine10 provided herein is not necessarily limited to a photolithography for semiconductor manufacturing. Thelithography machine10, for example, can be used as an LCD photolithography system that exposes a liquid crystal display work piece pattern onto a rectangular glass plate or a photolithography system for manufacturing a thin film magnetic head. Accordingly, the term “work piece” is generically used herein to refer to any device that may be patterned using lithography, such as but not limited to wafers or LCD substrates.

Theapparatus frame12 supports the components of thelithography machine10. Theapparatus frame12 illustrated inFIG. 1 supports thereticle stage assembly18, thewafer stage assembly20, theoptical assembly16 and theillumination system14 above the mountingbase32.

Theillumination system14 includes anillumination source34 and an illuminationoptical assembly36. Theillumination source34 emits a beam (irradiation) of light energy. The illuminationoptical assembly36 guides the beam of light energy from theillumination source34 to theoptical assembly16. The beam illuminates selectively different portions of thereticle28 and exposes thewafer30. InFIG. 1, theillumination source34 is illustrated as being supported above thereticle stage assembly18. Typically, however, theillumination source34 is secured to one of the sides of theapparatus frame12 and the energy beam from theillumination source34 is directed to above thereticle stage assembly18 with the illuminationoptical assembly36.

Theillumination source34 can be a g-line source (436 nm), an i-line source (365 nm), a KrF excimer laser (248 nm), an ArF excimer laser (193 nm) or a F₂laser (157 nm). Alternatively, theillumination source34 can generate an x-ray.

Theoptical assembly16 projects and/or focuses the light passing through thereticle28 to thewafer30. Depending upon the design of thelithography machine10, theoptical assembly16 can magnify or reduce the image illuminated on thereticle28. Theoptical assembly16 need not be limited to a reduction system. It could also be a 1× or greater magnification system.

Also, with an exposure work piece that employs vacuum ultra-violet radiation (VUV) ofwavelength 200 nm or lower, use of a catadioptric type optical system can be considered. Examples of a catadioptric type of optical system are disclosed in Japanese Laid-Open Patent Application Publication No. 8-171054 and its counterpart U.S. Pat. No. 5,668,672, as well as Japanese Laid-Open Patent Publication No. 10-20195 and its counterpart U.S. Pat. No. 5,835,275. In these cases, the reflecting optical system can be a catadioptric optical system incorporating a beam splitter and concave mirror. Japanese Laid-Open Patent Application Publication No. 8-334695 and its counterpart U.S. Pat. No. 5,689,377 as well as Japanese Laid-Open Patent Application Publication No. 10-3039 and its counterpart U.S. Pat. No. 873,605 (Application Date: Jun. 12, 1997) also use a reflecting-refracting type of optical system incorporating a concave mirror, etc., but without a beam splitter, and also can be employed with this invention. The disclosures of the above-mentioned U.S. patents and applications, as well as the Japanese Laid-Open patent application publications are incorporated herein by reference in their entireties.

Thereticle stage assembly18 holds and positions thereticle28 relative to theoptical assembly16 and thewafer30. In one embodiment, thereticle stage assembly18 includes areticle stage38 that retains thereticle28 and a reticlestage mover assembly40 that moves and positions thereticle stage38 andreticle28.

Eachstage mover assembly40,44 can move therespective stage38,42 with three degrees of freedom, less than three degrees of freedom, or more than three degrees of freedom. For example, in alternative embodiments, eachstage mover assembly40,44 can move therespective stage38,42 with one, two, three, four, five or six degrees of freedom. The reticlestage mover assembly40 and the work piecestage mover assembly44 can each include one or more movers, such as rotary motors, voice coil motors, linear motors utilizing a Lorentz force to generate drive force, electromagnetic movers, planar motors, or some other force movers.

In photolithography systems, when linear motors (see U.S. Pat. Nos. 5,623,853 or 5,528,118 which are incorporated by reference herein in their entireties) are used in the wafer stage assembly or the reticle stage assembly, the linear motors can be either an air levitation type employing air bearings or a magnetic levitation type using Lorentz force or reactance force. Additionally, the stage could move along a guide, or it could be a guideless type stage that uses no guide.

Alternatively, one of the stages could be driven by a planar motor, which drives the stage by an electromagnetic force generated by a magnet unit having two-dimensionally arranged magnets and an armature coil unit having two-dimensionally arranged coils in facing positions. With this type of driving system, either the magnet unit or the armature coil unit is connected to the stage base and the other unit is mounted on the moving plane side of the stage.

Movement of the stages as described above generates reaction forces that can affect performance of the photolithography system. Reaction forces generated by the wafer (substrate) stage motion can be mechanically transferred to the floor (ground) by use of a frame member as described in U.S. Pat. No. 5,528,100 and Japanese Laid-Open Patent Application Publication No. 8-136475. Additionally, reaction forces generated by the reticle (mask) stage motion can be mechanically transferred to the floor (ground) by use of a frame member as described in U.S. Pat. No. 5,874,820 and Japanese Laid-Open Patent Application Publication No. 8-330224. The disclosures of U.S. Pat. Nos. 5,528,100 and 5,874,820 and Japanese Paid-Open Patent Application Publication Nos. 8-136475 and 8-330224 are incorporated herein by reference in their entireties.

Themeasurement system22 monitors movement of thereticle28 and thewafer30 relative to theoptical assembly16 or some other reference. With this information, thecontrol system24 can control thereticle stage assembly18 to precisely position thereticle28 and the workpiece stage assembly20 to precisely position thewafer30. The design of themeasurement system22 can vary. For example, themeasurement system22 can utilize multiple laser interferometers, encoders, mirrors, and/or other measuring devices.

Thecontrol system24 receives information from themeasurement system22 and controls thestage assemblies18,20 to precisely position thereticle28 and thewafer30. Additionally, thecontrol system24 can control the operation of the components of theenvironmental system26. Thecontrol system24 can include one or more processors and circuits.

Theenvironmental system26 controls the environment in a gap (not shown) between theoptical assembly16 and thewafer30. The gap includes an imaging field. The imaging field includes the area adjacent to the region of thewafer30 that is being exposed and the area in which the beam of light energy travels between theoptical assembly16 and thewafer30. With this design, theenvironmental system26 can control the environment in the imaging field. The desired environment created and/or controlled in the gap by theenvironmental system26 can vary accordingly to thewafer30 and the design of the rest of the components of thelithography machine10, including theillumination system14. For example, the desired controlled environment can be a fluid such as water. Alternatively, the desired controlled environment can be another type of fluid such as a gas. In various embodiments, the gap may range from 0.1 mm to 10 mm in height between top surface of thewafer30 and the last optical element of theoptical assembly16.

In one embodiment, theenvironmental system26 fills the imaging field and the rest of the gap with an immersion fluid. The design of theenvironmental system26 and the components of theenvironmental system26 can be varied. In different embodiments, theenvironmental system26 delivers and/or injects immersion fluid into the gap using spray nozzles, electro-kinetic sponges, porous materials, etc. and removes the fluid from the gap using vacuum pumps, sponges, and the like. The design of theenvironmental system26 can vary. For example, it can inject the immersion fluid at one or more locations at or near the gap. Further, the immersion fluid system can assist in removing and/or scavenging the immersion fluid at one or more locations at or near thework piece30, the gap and/or the edge of theoptical assembly16. For additional details on various environmental systems, see U.S. provisional patent applications 60/462,142 entitled “Immersion Lithography Fluid Control System” filed on Apr. 9, 2003, 60/462,112 entitled “Vacuum Ring System and Wick Ring System for Immersion Lithography” filed on Apr. 10, 2003, 60/500,312 entitled “Noiseless Fluid Recovery With Porous Material” filed on Sep. 3, 2003, and 60/541,329 entitled “Nozzle Design for Immersion Lithography” filed on Feb. 2, 2004, all incorporated by reference herein in their entireties.

Referring toFIG. 2, a cross section of a lithography machine illustrating one embodiment of the invention is shown. Thelithography machine200 includes aoptical assembly16 and astage assembly202 that includes a wafer table204 and awafer stage206. The wafer table204 is configured to support a wafer208 (or any other type of work piece) under theoptical assembly16. Anenvironmental system26, surrounding theoptical assembly16, is used to supply and removeimmersion fluid212 from the gap between thewafer208 and the last optical element of theoptical assembly16. A workpiece exchange system216, including a wafer loader218 (i.e., a robot) and an alignment tool220 (i.e., a microscope and CCD camera), is configured to remove thewafer208 on the wafer table204 and replace it with a second wafer. This is typically accomplished using thewafer loader218 to lift and remove thewafer208 from the wafer table204. Subsequently, the second wafer (not shown) is placed onto thewafer chuck218, aligned using thealignment tool220, and then positioned under theoptical assembly16 on the wafer table204.

With this embodiment, thewafer stage206 includes an immersionfluid containment system214 that is configured to maintain theimmersion fluid212 in the gap adjacent to the last optical element of theoptical assembly16 during wafer exchange. The immersionfluid containment system214 includes apad222 that is adjacent to the wafer table204. Asupport member224, provided between thepad222 and thewafer stage206, is used to support thepad222. The wafer table204 has a flat upper surface that is coplanar with a surface of thewafer208. Thepad222 also has a flat upper surface that is coplanar with the upper surface of the wafer table204 and the wafer surface. Thepad222 is arranged adjacent to the wafer table204 with a very small gap (e.g., 0.1-1.0 mm) so that theimmersion fluid212 is movable between the wafer table204 and thepad222 without leaking. During a wafer exchange, thewafer stage206 is moved in the direction ofarrow226 so that thepad222 is positioned under theoptical assembly16 in place of the wafer table204, maintaining the fluid in the gap or maintaining the size of the fluid gap. After the new wafer has been aligned, the wafer stage is moved back to its original position so that thepad222 is removed from the gap as the second wafer is positioned under theoptical assembly16. In various embodiments, thepad222 is disposed continuously adjacent to the wafer table204 with no gap. Vertical position and/or tilt of the wafer table204 can be adjusted so that the wafer table surface is coplanar with the pad surface, before the wafer table204 is moved out from under theoptical assembly16. Maintaining the gap between thepad222 and theoptical assembly16 is not limited to just a wafer exchange operation. Thepad222 can be large enough to maintain theimmersion fluid212 in the space between thepad222 and theoptical assembly16 during an alignment operation or a measurement operation. In those operations, a part of the area occupied by theimmersion fluid212 may be on the upper surface of the wafer table204.

Referring toFIGS. 3A and 3B, a cross section and a top down view of another immersion lithography machine according to another embodiment of the present invention are shown. Thelithography machine300 includes anoptical assembly16 and astage assembly302 that includes a wafer table304 and awafer stage306. The wafer table304 is configured to support a wafer308 (or any other type of work piece) under theoptical assembly16. Anenvironmental system26, surrounding theoptical assembly16, is used to supply and removeimmersion fluid312 from the gap between thewafer308 and the lower most optical element of theoptical assembly16. A workpiece exchange system316, including awafer loader318 and analignment tool320, is configured to remove thewafer308 on the wafer table304 and replace it with a second wafer. This is accomplished using thewafer loader318 to remove thewafer308 from the wafer table. Subsequently, the second wafer (not shown) is placed onto thewafer chuck318, aligned using thealignment tool320, and then positioned under theoptical assembly16. As best illustrated inFIG. 3B, a set ofmotors322 are used to move thewafer assembly302 including the wafer table304 andwafer stage306 in two degrees of freedom (X and Y) during operation. As noted above, themotors322 can be any type of motors, such as linear motors, rotary motors, voice coil motors, etc.

Theimmersion lithography machine300 also includes an immersionfluid containment system324 that is configured to maintain theimmersion fluid312 in the space below theoptical assembly16 while the wafer table304 is away from under the optical assembly. The immersionfluid containment system324 includes apad326, amotor328, and acontrol system330. Thepad326 can be positioned adjacent to theoptical assembly16 and the wafer table304. The wafer table304 has a flat upper surface that is coplanar with a surface of thewafer308. Thepad326 has a flat upper surface that is coplanar with the upper surface of the wafer table304 and the wafer surface. Thepad326 is movable in the X and Y directions using themotor328, which is controlled by thecontrol system330. Themotor328 can be any type of motor as well as themotors322. Thepad326 is positioned under theoptical assembly16 when the wafer table304 (the wafer stage306) is away from under theoptical assembly16. During a wafer exchange, the wafer table304 moves away from theoptical assembly16. Simultaneously, thecontrol system330 directs themotor328 to movepad326 under theoptical assembly16, replacing the wafer table304. Thepad326 thus retains theimmersion fluid312 within the gap under theoptical assembly16. After the new wafer has been aligned using thealignment tool320, the wafer table304 is repositioned under theoptical assembly16. At the same time, thecontrol system330 directs themotor328 to retract thepad326 from the gap, preventing the escape of theimmersion fluid312. In the wafer exchange operation, thecontrol system330 moves the wafer table304 and thepad326 with a small gap between the wafer table304 and thepad326, while theimmersion fluid312 below theoptical assembly16 moves between the wafer table304 and thepad326. The immersionfluid containment system324 thus maintains theimmersion fluid312 from the gap during wafer exchange. In this embodiment, the wafer table304 (the wafer stage306) and thepad326 are movable separately. Therefore, the wafer table304 is movable freely while theimmersion fluid312 is maintained in the space between thepad326 and theoptical assembly16. In various embodiments of the invention, thecontrol system330 may be a separate control system or it can be integrated into the control system used to control themotors322 for positioning thewafer stage306 and wafer table304. Vertical position and/or tilt of at least one of the wafer table304 and thepad326 may be adjusted so that the wafer table surface is coplanar with the pad surface, before the wafer table is moved out from under theoptical assembly16. The operation, in which the wafer table304 is away from theoptical assembly16, is not necessarily limited to a wafer exchange operation. For example, an alignment operation, a measurement operation or other operation may be executed while maintaining theimmersion fluid312 in the space between thepad326 and theoptical assembly16.

Referring toFIGS. 4A and 4B, two cross sections of an immersion lithography machine are shown. Thelithography machine400 includes anoptical assembly16 and astage assembly402 that includes a wafer table404 and awafer stage406. The wafer table404 is configured to support a wafer408 (or any other type of work piece) under theoptical assembly16. An environmental system26 (410), surrounding theoptical assembly16, is used to supply and removeimmersion fluid412 from the gap between thewafer408 and the lower most optical element of theoptical assembly16. A workpiece exchange system416, including awafer loader418 and analignment tool420, is configured to remove thewafer408 on the wafer table404 and replace it with a second wafer. This is accomplished using thewafer loader418 to remove thewafer408 from the wafer table404. Subsequently, the second wafer (not shown) is placed onto thewafer chuck418, aligned using thealignment tool420, and then positioned under theoptical assembly16 as illustrated in theFIG. 4A.

Theimmersion lithography machine400 also includes an immersionfluid containment system424 that is configured to maintain theimmersion fluid412 in the space below theoptical assembly16 while the wafer table404 is away from under theoptical assembly16. The immersionfluid containment system424 includes apad426, afirst clamp428 provided on theoptical assembly16 and asecond clamp430 provided on the wafer table404. When theimmersion fluid412 is between theoptical assembly16 and the wafer table404 (or the wafer408), thepad426 is held by thesecond clamp430 in place on the wafer table404. When the wafer table404 is away from theoptical assembly16, for example during a wafer exchange operation, thepad426 is detached from the wafer table404 and held by thefirst clamp428 to maintain theimmersion fluid412 between theoptical assembly16 and thepad426. The wafer table404 has a flat upper surface that is coplanar with a surface of thewafer408. Thepad426 held on the wafer table404 also has a flat upper surface that is coplanar with the upper surface of the wafer table404 and the wafer surface. Therefore, theimmersion pad426 andwafer408 can be moved under the optical assembly without the immersion fluid leaking. In various embodiments, theclamps428 and430 can be vacuum clamps, magnetic, electro-static, or mechanical.

As best illustrated inFIG. 4A, thepad426 is positioned on the wafer table404 during exposure of thewafer408. Thesecond clamp430 is used to hold thepad426 in place on the table404 during the wafer exposure. During a wafer exchange as illustrated inFIG. 4B, the wafer table404 is moved in the direction ofarrow432 so that thepad426 is positioned under theoptical assembly16 in place of thewafer408. When this occurs, thesecond clamp430 holding thepad426 to the wafer table404 is released whilefirst clamp428 clamps thepad426 to theoptical assembly16. As a result, theimmersion fluid412 is maintained under the optical assembly while thewafer408 is exchanged. After the new wafer has been aligned, the wafer table404 is moved in the direction oppositearrow432 so that the new wafer is positioned under the optical assembly. Prior to this motion, thefirst clamp428 is released while thesecond clamp430 again clamps thepad426 to the wafer table404. In this embodiment, the wafer table404 is freely movable while thepad426 is clamped by thefirst clamp428.

In various embodiments, the operation, in which thepad426 is clamped by thefirst clamp428, is not limited to only a wafer exchange operation. An alignment operation, a measurement operation, or any other operation can be executed while theimmersion fluid412 is maintained in the space between theoptical assembly16 and thepad426 clamped by thefirst clamp428. Also, theclamp428 can be provided on theframe12 or other support member, and theclamp430 can be provided on thewafer stage406. Thepad426 can be held on a movable member other than thestage assembly402.

FIGS. 5A and 5B are top down views of two different twin stage immersion lithography systems according to other embodiments of the present invention. For the basic structure and operation of the twin stage lithography systems, see U.S. Pat. No. 6,262,796 and U.S. Pat. No. 6,341,007. The disclosures of U.S. Pat. No. 6,262,796 and U.S. Pat. No. 6,341,007 are incorporated herein by reference in their entireties. In both embodiments, a pair of wafer stages WS1 and WS2 are shown.Motors502 are used to move or position the two stages WS1 and WS2 in the horizontal direction (in the drawings), whereasmotors504 are used to move or position the stages WS1 and WS2 in the vertical direction (in the drawings). Themotors502 and504 are used to alternatively position one stage under theoptical assembly16 while a wafer exchange and alignment is performed on the other stage. When the exposure of the wafer under theoptical assembly16 is complete, then the two stages are swapped and the above process is repeated. With either configuration, the various embodiments of the invention for maintaining immersion fluid in the gap under theoptical assembly16 as described and illustrated above with regard toFIGS. 2 through 4, can be used with either twin stage arrangement. With regard the embodiment ofFIG. 2 for example, each wafer stage SW1 and SW2 of eitherFIG. 5A or5B can be modified to include apad222 and asupport member224. With regard to the embodiment ofFIG. 3, asingle pad326,motor328, andcontrol system330 could be used adjacent to theoptical assembly16. Thepad326 is movable separately from the stages SW1 and SW2. During the time when stages SW1 and SW2 are to be swapped, thepad326 is moved to under theoptical assembly16 to maintain theimmersion fluid312 below theoptical assembly16. Finally with the embodiment ofFIG. 4, a detachable single pad can be used. During the time when stages SW1 and SW2 are to be swapped, thepad426 is used to maintain the immersion fluid in the gap as illustrated inFIG. 4B. On the other hand during exposure, the pad is clamped onto the wafer table on the wafer stage that is being exposed. In this manner, only a single pad is needed for the two stages WS1 and WS2. Alternatively, as described below, the second stage can also be used as the pad.

Referring toFIG. 6A, a top down view of a twin stage lithography machine illustrating one embodiment of practicing the invention is shown. In this embodiment, theimmersion lithography system600 includesfirst stage604 andsecond stage606. The two stages are moved in the X and Y directions bymotors602. In this embodiment, thestages604 and606 themselves are used to contain the immersion fluid in the gap. For example as shown in the Figure, thefirst stage604 is positioned under theoptical assembly16. When it is time for the work piece to be exchanged, themotors602 are used to position thesecond stage606 with a second work piece adjacent to thefirst stage604. With the two stages positioned side-by-side, they substantially form a continuous surface. Themotors602 are then used to move the two stages in unison so that thesecond stage604 is position under theoptical assembly16 and the first stage is no longer under theoptical assembly16. Thus when the first work piece is moved away from theoptical assembly16, the immersion fluid in the gap is maintained by thesecond stage606, which forms the substantially continuous surface with the first stage. In various alternative embodiments, thesecond stage606 could also be a “pad” stage that contains a pad that is used to maintain the immersion liquid in the gap while a second work piece is being placed onto thefirst stage604. Similarly, the motor arrangement shown in eitherFIG. 5A or5B could be used.

Referring toFIGS. 6B-6E, a series of diagrams illustrating a work piece exchange according to one embodiment of the invention is illustrated.FIG. 6B shows a wafer onstage604 after exposure is completed.FIG. 6C shows thesecond stage606 in contact (or immediately adjacent) with thefirst stage604 under theoptical assembly16.FIG. 6C shows a transfer taking place, i.e., thesecond stage606 is positioned under theoptical assembly16. Finally, inFIG. 6E, thefirst stage604 is moved away from theoptical assembly16. As best illustrated inFIGS. 6C and 6D, the twostages604 and606 provide a continuous surface under theoptical assembly16 during a transfer, thus maintaining the immersion fluid in the gap. In the embodiment shown, thesecond stage606 is a pad stage. This stage, however, could also be a work piece stage as noted above.

In the various embodiments described above, the pad can be made of a number of different materials, such as ceramic, metal, plastic. These materials may also be coated with Teflon according to other embodiments. The size of the pad also should be sufficient to cover the area occupied by the immersion fluid. In the various embodiments described above, the surface of the last optical element of theoptical assembly16 is constantly under immersion fluid environment, preventing the formation of a fluid mark (e.g. “a water mark”).

Semiconductor wafers can be fabricated using the above described systems, by the process shown generally inFIG. 7A. Instep701 the work piece's function and performance characteristics are designed. Next, instep702, a mask (reticle) having a pattern is designed according to the previous designing step, and in a parallel step703 a wafer is made from a silicon material. The mask pattern designed instep702 is exposed onto the wafer fromstep703 instep704 by a photolithography system described hereinabove in accordance with the invention. Instep705 the semiconductor work piece is assembled (including the dicing process, bonding process and packaging process); finally, the work piece is then inspected instep706.

FIG. 7B illustrates a detailed flowchart example of the above-mentionedstep704 in the case of fabricating semiconductor work pieces. InFIG. 7B, in step711 (oxidation step), the wafer surface is oxidized. In step712 (CVD step), an insulation film is formed on the wafer surface. In step713 (electrode formation step), electrodes are formed on the wafer by vapor deposition. In step714 (ion implantation step), ions are implanted in the wafer. The above mentioned steps711-714 form the preprocessing steps for wafers during wafer processing, and selection is made at each step according to processing requirements.

At each stage of wafer processing, when the above-mentioned preprocessing steps have been completed, the following post-processing steps are implemented. During post-processing, first, in step715 (photoresist formation step), photoresist is applied to a wafer. Next, in step716 (exposure step), the above-mentioned exposure work piece is used to transfer the circuit pattern of a mask (reticle) to a wafer. Then in step717 (developing step), the exposed wafer is developed, and in step718 (etching step), parts other than residual photoresist (exposed material surface) are removed by etching. In step719 (photoresist removal step), unnecessary photoresist remaining after etching is removed.

Multiple circuit patterns are formed by repetition of these preprocessing and post-processing steps.

While the particular lithography machines as shown and disclosed herein are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative embodiments of the invention, and that the invention is not limited to these embodiments.

Claims (18)

What is claimed is:

1. A lithographic projection apparatus comprising:

a substrate table on which a substrate is held;

a projection system that projects a patterned beam onto a target portion of the substrate held by the substrate table, an immersion liquid, through which the beam is to be projected, being in a space between the projection system and the substrate; and

a flat pad that keeps the projection system in contact with the immersion liquid when the substrate, at least while held on the substrate table, comes out of contact with the immersion liquid, the flat pad being separate from the substrate table.

2. An apparatus according toclaim 1, wherein the flat pad is positionable opposite the projection system such that the immersion liquid can be confined between the projection system and the flat pad.

3. An apparatus according toclaim 2, further comprising an attachment device that releasably attaches the flat pad over a final optical element of the projection system.

4. An apparatus according toclaim 3, wherein the attachment device comprises a vacuum outlet that attracts the flat pad toward the projection system.

5. An apparatus according toclaim 2, wherein the substrate table comprises a holding device that releasably holds the flat pad to the substrate table.

6. An apparatus according toclaim 2, wherein, in a stowed position, the flat pad has a primary surface substantially co-planar with a surface of the substrate facing the projection system.

7. An apparatus according toclaim 2, wherein the lithographic apparatus comprises a controller that moves the substrate table relative to the projection system so that the flat pad confines the immersion liquid between the flat pad and the projection system.

8. An apparatus according toclaim 1, wherein the flat pad has a primary surface substantially co-planar with a surface of the substrate facing the projection system and is closely adjacent to an edge of the substrate.

9. An apparatus according toclaim 1, further comprising a structure extending along at least a part of a boundary of the space between the projection system and the substrate table and wherein the flat pad, when keeping the projection system in contact with the immersion liquid, is positioned to cover the structure.

10. An apparatus according toclaim 1, wherein the flat pad keeps the projection system in contact with the immersion liquid when the substrate is moved away from under the projection system.

11. A device manufacturing method comprising:

providing an immersion liquid to a space between a projection system and a substrate;

projecting a patterned beam of radiation, through the immersion liquid, onto a target portion of the substrate using the projection system; and

maintaining the projection system in contact with the immersion liquid when the substrate, at least while on a substrate table, comes out of contact with the immersion liquid by placing a flat pad, which is separate from the substrate table, adjacent to the projection system in place of the substrate.

12. A method according toclaim 11, wherein maintaining the projection system in contact with liquid comprises positioning the flat pad on a side opposite the projection system such that liquid is confined between the projection system and the flat pad.

13. A method according toclaim 12, further comprising releasably attaching the flat pad over a final optical element of the projection system.

14. A method according toclaim 13, wherein releasably attaching comprises attaching the flat pad using vacuum.

15. A method according toclaim 12, wherein the flat pad, when keeping the projection system in contact with the immersion liquid, is positioned to cover a structure that extends along at least a part of a boundary of the space between the projection system and the substrate table.

16. A method according toclaim 12, comprising moving the substrate table relative to the projection system so that the flat pad confines the immersion liquid between the flat pad and the projection system.

17. A method according toclaim 11, comprising providing the immersion liquid to a space between a final lens of the projection system and the substrate.

18. A method according toclaim 11, wherein the maintaining comprises maintaining the projection system in contact with the immersion liquid after the substrate has been moved away from under the projection system.

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